The present invention relates to a sewing machine controlling apparatus, which starts and stops a sewing machine or controls its variable speed in accordance with the position of an adjusting means for setting a sewing machine speed.
Conventionally, a system was mainly adopted of converting the position of the adjusting means of a sewing machine controlling apparatus into analog signals so as to make the analog signals into speed setting signals, and composing the speed controlling portion of analog operation around an OP amplitude circuit.
However, in recent years the development in digital IC's, etc., with microcomputers as central components is conspicuous. The speed controls have been gradually digitized for improvements in terms of cost or reliability. Thus, the detection signals of the adjusting means are naturally required to be digitized. When the pedal of the sewing machine is used as the adjusting means, various systems are used to detect and generate digital signals corresponding to the movement thereof.
However, some digital systems, which are common among the various systems, have a fatal disadvantage in that a boundary exists where the signal changes without fail; the changes are caused between two adjacent signal values due to the variations of the sewing machine, when the pedal has been positioned on the condition of the boundary, so as to considerably vary the speed of the sewing machine, and thus making it impossible to be put into practical use.